The implications of consuming JavaScript modules with Google Closure are huge: the external libraries used in a ClojureScript project are no longer just prepended to the generated bundle, but can now be subjected to all of Closure Compiler’s optimizations, including dead code elimination and, in projects that take advantage of code splitting, cross module code motion. For example, in our tests React is appreciable smaller (~16%) under Closure’s advanced compilation than it would be using existing popular JavaScript tooling . Additionally, if you have a mixed codebase of ClojureScript and JavaScript, not only can you now seamlessly consume those JavaScript portions of your code (including e.g. JSX transformations!